The aims of this project are: I. Improve the blue field entoptic simulation technique and study the effect of contrast, sharpness, and distribution of simulated leukocytes on the determination of entoptically seen leukocyte speed and number. II. In normal subjects, investigate macular blood flow and its regulation in response to alterations in perfusion pressure and inspired O2 and CO2 concentrations. III. In diabetes, determine (a) whether macular blood flow and its regulation is abnormal in maculopathy, (b) the effect of panretinal photocoagulation on macular blood flow and its regulation and whether the occurrence of macular edema is associated with abnormalities of flow and regulation, (c) whether the blue field entoptic test can be used as a predictor of post-treatment visual acuity in patients undergoing focal photocoagulation for diabetic macular edema, and (d) whether abnormal autoregulation can be correlated with the progression of retinopathy to preproliferative and proliferative stages. IV. In open angle glaucoma, determine (a) the relationship between macular blood flow and perfusion pressure, (b) the effect of topically applied timolol and epinephrine on macular blood flow. V. Develop a simulation of the entoptic observation of the perifoveal microvasculature and investigate, in normal subjects, the size of the foveal avascular zone and the density of the parafoveal capillary network. It is hoped that these studies will help to understand the physiology of the macular retinal microcirculation and to quantify the changes in retinal blood flow and its regulation in diabetes mellitus and open angle glaucoma.